Wave translation system



Dec.^2l, 1937; H s -BLACK 'A 2,102,670 f wAvE TRANSLATION SYSTEM' original Filed Aug. a, 1928 e sheets-sheet;

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' WAVE TRANSLATION SYSTEM f l Original Filed Aug. 8, 1923 6 Sheets-Sheet 5 /Nl/E/VTUR HARULD .5. BLACK Dec. 21, 1937. H, s /BLACK y 2,102,670

, wAvE TRANSLATION SYSTEM j Original Filed Aug. 8, 1923 6 Sheets-Sheet 4 A TTUH/VEY Dec. 2l, 1937. H. s. BLACK WAVE TRANSLATION SYS TEM 6 Sheets-Sheet 5 '"Urginal Filed Aug. 8, 1923 H. 5. BLACK Dea. 21,1937. H. s. BLACK 2,102,670`

wAvE TRANSLATION gYsTEM- Original Filed Aug. I8, 1923 6 Sheets-Sheet 6 www /A/i/E/VTOBQD H.' 5. BLA cK vtime Dee. 21, 1931 l UNITED STATES Y PATENT OFFICE Bell Telephone Laboratories,

Incorporated,

New York, N. Y., a corporation of New York original applicativa August a, 192s, serial No.

Divided and this application December 3, 1929, Serial No. 411,223. Renewed ctober 21, 1932. In CanadaMay 21, 1929 s2 claims.

j power output of vacuumtubes or electric spacel l0 discharge devices tends to increase distortion of isignaling or other waves transmittedby the devices, and tends to lower the gain of the circuits of the devices. s A

At high values of output power, gain may be- `corne so low that further increase of input amplitude or decrease of output impedance pro-l duces no further increase of power output.

However, in. many 'applications of vacuum tubes, long before the power output of t'he tubev 0 reaches the maximum value that the tube is capable of delivering or seriously lowers the gain of the tube circuit, distortion becomes so great as to render further increase of output power in- ,advisable Representativeinstances in the iield of application of amplifiers, for example, are voice frequency telephone repeaters. 'carrier frequency amplifiers common to a'plurality of signalingchannels in carrier wave multiplex signaling systems, amplifiers for public address systems, am-

0- pliers for `reproducing music from records, power In each such instance, the higher the quality 'or transmission required,l or in other words, the less the distortion permissible, thesooner is the maximum permissible outputl power reached, that 40 is, the lower ls the ratio of maximum permissible output power to the maximum output power that the tube or-tubes o f the ampliiler `stage is capable of delivering. Therefore, the higher the transmission quality demanded, themore inelciently n vhas the power capacity of the tube or tubes been neem-and consequently when both high trans-A mission quality and high output of power are rebe especially'great -because only a small fraction` (ci. 11s-44) of the total power that each tube is capable of delivering can be utilized. The present tendency in practice is toward higher and higher transmission Aquality, .and also the number of applications and installations requiring highoutput 5 power is rapidly increasing, and moreover, the tendency is toward higher quality even where enormous power is demanded and interference `or disturbances tending to introduce noise in the waves transmitted is great, as in transatlantic radio telephony. v

In general, the design limitations for vacuum tubes of the types commonly employed are such that the highest output power capacity of the tube is-obtained only at a. sacrifice of maximum gain obtainable, or of operating emciency, or of both.

' In the case of a carrier frenquency ampliiier common to a plurality of signaling channels in a carrier wave multiplex signaling system, the .tendency of the amplifier to modulate a wave of one frequency by a. wave of` another frequency, increases greatly with increase in., the output power, and there results therefore-a very large increase in crosstalk andjinterference between 25 the various channels, this increase being more serious the larger the number of channels.

Therefore, a major problem in devising vacuum tube systems, as for example vacuum tube amplier systems, is the securing of high output of power without attendant disadvantages, as for example without increase of first cost or decrease of operating eillciency of the systems, and 'especially in the case of vacuum tube amplifiers and repeste without sacrifice of quality of signal reproduction. Representative objects of the invention are (1 economically to increase the load carrying ca. pacity o'f wave translation systems, as for example, systems for amplifying electrical variations 4o with4 the sid ofelectric space discharge devices, (2) to controll modulation in such systems, (3) i to .amplify waves without modulation or other l distortion. 4) to facilitate the handling of large leads by electric space discharge devices, and 45 (5) to stabilize the functioning of systems com.- prising electric space discharge tubes, as for example to prevent variations of tubes or power from aiiecting gain.

In one speciilc aspect ythe inventionis a signal 50 vincrease the load carrying capacity of the systeml" wave amplifying systemofsty'pe claimedin my copending application Serial No. $08,871'. -filed April 22, 1932, for wave translation systems. In

systems of such type. fundamental or applied l components and distortion components produced in an amplifying device. as for example a vacuumtubeamplifiercircmt,aresofedbackas to reduce the magnitude of the distortion components of both'odd and even orders in the output circuit of the device fora given power output of fundamental and stabilize thel gain and In the above mentioned speciiic aspect o f the present invention, in obtaining reduction of dis tortlon, increase of gain stability and high load capacity in a system comprising an amplifying device, undesired reduction in the 'gain ofthe system is avoided by isolating the distortion components from the fundamental components and feeding back only the. distortion components when the gain of the device has no tendency tof depart from anormal or prescribed-value, and, when such tendency exists, so controlling feedback of fundamental components as to cause reductionL or. prevention of departure of the gain 'of the system from itsnormal or prescribed value.

Other objects and aspects ofthe invention will be apparent from the following description and claims.

Figs. 1 end z of the drawings arelcircult die! grams for .facilitating explanation of the invention; Fig. 3 shows a feed-back amplifier embodying one form of the invention; Figs. 3A, 3B and 3C are diagrams, and Fig. 3D -a set of curves tem of-the type o'f that shown in Fig. 5; and Figs.

for facilitating explanation'of the operation of the amplifier o f Fig. 3;,Flg. 3E shows a modifica'- tion of the'ampller of Fig. 3; Fig. 4 showsa feed-back amplifier embodying another form .of

the invention; Fig. 4A isa simplified circuit diagram ofthe ampliiier of Fig. 4, for facilitating explanation of the operation of that amplifier;

Fig. 5 shows a', modified form of the amplifier of Fig. '4: Fig. 6 shows a feed-back amplifier embodying another form of the invention; 'I shows a modified form of thel amplifier of Fig. 5,; Fig. 8 shows -a similarly modified form ol? the amplifier of Fis. 6; Fig. 9 shows another'modiijied form 'of the amplifier of Fig. 6; rFig. 10 shows a 'carrier frequency amplifier embodying principles of the invention; Figs. 11 and 12 show curves for facilitating explanation of the action of a sys- 3F, 4B and 6A show the circuits o f Figs. 3, 4 and 6 respectively with certain of the impedances gen-v 4 eralized; and Fig, 9A is a modification o'f Fig. 9.

The driving voltage in the plate circuit of .an amplifier is 180 out ofphase with the grid voltage which produces it.- For a feed-back ampli-v fier, it is desirable that there be available a voltage which ls directly proportional to, and in phase with, the driving voltage in the plate circuit. and

which is independent of-theimpedance ofthe.

work circuit. It will-be seen from-Fig. 1 and the derivationv below, that the voltage Ae, which is the drop across resistances KR and KRO, fulfills these three conditions.

In the figure, Ro is a resistance (for example,

thereslstance of the space discharge path between the plate and the vfilament of a three electrode vacuumtube) represents, as a generator, a source of voltage e (for example, the driving voltage -e produced in the 'discharge path by the,v grid voltage): and Z is an impedance (for ex-v ample, the impedance of the load circuit or work ciremt of the tube). Two resistances designated Clhecircuit of Fig. 2"is like that of Fig. 1, ex

' cept that a resistancegR- is bridged acrossfKRo andKR. The current components owin'g in the variousparts ofthe 'circuit' ofFig. 2 are'indicated by the arrows andtheiraccompanying letters i with 'the appropriate subscripts. However.

.in' Fig. `2 the currents indicated by i1. fraud t1+z 'andthe voltage-indicated by Ae are not in general of the samemagnltudes as in Flg. l. When a resistance Ris connected across KR vand KR, the Voltage-Are' stilll fllllls the three conditions mentionedabove. Referring to Fig. 2 thisis demonstrated as follows:

Aq K l .R

Fig. 3 shows one way in which this voltage may .be utilized. In this figure a three-electrode, electric space discharge amplifying device I has an anode-cathode space-discharge path of resistance Ro, which is associated with resistances KRo, KR, and R, and impedance Z, inthe manner of resistance R in Figs. 1 and 2.v The plate-illament resistance Ro is the reciprocal of the slope of thestatic characteristic of plate current versus plate voltage of the discharge device at the so called operating point, as explained in the following ar -ticles by John R. Carson in thel Proceedings of the Institute of Radio Engineers: 'I'heory. of Three Element Vacuum Tube, vol. 7, pp. 1874200,

A prll 1919; The Equivalent Circuit of the Vacderivation mentioned above is as follows:l

uum Tube Modulator. vol. 9, pp. 243-249, June 1921. (That is,

Rn bef,

where ip and ep are instantaneous plate current and voltage, respectively.) In Fig. 3 the'impedance Z is the primary-to-secondary impedance of output transformer 2 which. together with circuit 3 connected to the secondary wind-- ing of the transformer, forms the load or work circuit for the device I. An input transformer 4 impresses .waves yfrom circuit 5 upon the grid of the device I. These waves may be, for example,

.voice waves, or` voice modulated carrier waves for transmission over carrier wave wire transmission systems or to radio transmitting antennae or waves received over such systems. The usual plate, filament. and grid batteries are shown at 6, 'I and l. A circuit corresponding to the resistance R, of Fig. 2 and comprising the secondary winding .or secondary-to-primary imi pedante Roi of transformer 4, a resistapp. a blocking condenser s m m.: across the resisten -a connected to the junction of and Rui.. The condenser is a blocking condenser o f large' capacity, for preventing batteries 6 and 1 from applying steady voltage to the grid. The circuit through whichbattery 6 supplies plate current for the place of the galvanometer and E represents a source of voltage E which is applied through a resistance of (x4-Roi) that forms the input diagonal or feed-back diagonal of the bridge. For the condition of balance, it is evident that there is no current in Z due to E, the driving voltage in the grid circuit.

` There is some voltage V, from grid to filament. Due to V, there will be a driving voltage /iV in the plate circuit, with relative polarity as shown by the plus and minus signs. The presence of this voltage is indicated in Fig. 3A by generator MV.

To investigate the effect of the two generators or voltages E and MV- acting simultaneously, use

' is made of the principle of superposition. This principle is -that the current which iiows at any point in a circuit, or the difference vof potential which is established between' any two points in a circuit, due to the vsimultaneous action o-f a group of E. M. F.s located at the same or various points in a circuit, is the algebraic sum of the component currents at the rst point, or the component diierences of potential between the latter two points, which would be established by the in-. dividual E. M. F.s actingalone.

Due to E alone, there will be a voltage from grid to iilament, V1 equal to directly from the configuration of the specic circuit shown, but, though special to that particular configuration, are given in order to present a con- Y crete illustration .of the jsigniflcance o f V1, V2

That is, the voltage in the grid circuit (and hence the current in the` output impedancevZ) is reduced from what it would be if there were no feedback action, and the impedance relations were the same, by a factor It will now be shown that any distortion as for example modulation product) produced in the tube is also reduced by the same factor.

Consider the circuit of Fig. 3B. Let any primary distortion voltage produced in the tube be represented as a driving voltage 0, in the plate circuit. Let'the voltage drop between the grid and the filament, resulting from the distortion produced in the tube be Vo. This sets up another driving voltage in the plate circuit, MVO, with polarity as shown. As before,

That is, the final, or resultant, driving distortion voltage in the plate circuit is reducedby a factor from what it would be without feedback action.

It will be noted that due to the .configuration of the elements of the circuit, if a generator is assumed in series with Z, no current will ow in the branch wl-R01. Hence the impedance of the'amplier as seen from theload' or work circuit Z is the same as it would be without regeneration, and is independent of the shunt resistance :nfl-R01.

Now to return to a. consideration of the gain of the circuit, by the feed-back action the gain is stabilized with respect to variations of tubes and power. If due to any cause, thc/i of the tube is reduced, which would reduce the gain, the effective voltageon the grid is increased. Similarly, variations in Ro are stabilized. The curves 'of Fig. 3D, which are plotted from observed data, show that by the feedback action the load carrying capacity of the amplifier is substantially in'- creased, the variation of gain with load is reduced, and the ratio of the power output of secondA v harmonic to the power'output o'f fundamental is'` The curves Vfor operation Without feedback are for cpimproved or decreased about 12 decibels.

eration with the right hand side of condenser 9 disconnected from the ljunction of R and KR and diagonal is so high that substituting an equal resistance across the path through KR and KRO would not affect the operation of the circuit. Thus, the curves for operation -without feedback are forv operation with the external .grid-to-lament impedance and the external plateto-la` ment impedance for the tube the same as in oper-- .l ation with feedback. i

sol

y'it

The circuit of Fig. 3 can be modified to comprisea plurality of tubes connected in cascade, in which case n represents the total amplification from a voltage across the grid of the rst tube to a driving voltage in the plate of the last tube. For example, Fig. 3E shows one'such modied circuit, with tandem connected tubes la, Ib, and Ic replacing the tube I of Fig. 3. If the number of tubes be even instead of odd, then an odd number of phase reversals in addition to thosev produced by the tubes themselves should be produced, as for example by the introduction of an interstage or other transformer with its windings poled to reverse the phase of waves passing through vthe transformer.

In Fig. 3A consider voltage V3. l being contributed to by both E and nV, and these voltages tend to oppose each other. 4It is possible, therefore, by suitable adjustment of the circuit elements, notably to make Va=0. The value of :c to accomplish this may be found as follows:

In Fig. 3C, V=(Vo1tage drop across x)i-V3 ..V= (Voltage drop across x) since V3=0 Similarly Vr-[Voltage drop across (R4-R0 )]{-V3 =(Voltage drop across R-l-Ro) The current through a: must equal the current through R-I-Ro, for since V3=0, no current ows through (KR-I-KRO).

'I'his means that if is given the value and a voltage is applied to the circuit in series with R01, no voltage is produced across the feedback diagonal of the bridge. (That is, V3 in Fig. 3A is zero.) This does not apply to distortion voltages, since theseare present in the plate circuit, but not in the grid circuit; i. e., only, one generator is'acting. By giving :n the value we have two points (the ends of the feed-back diagonal) across which the vpotential corresponding to the fundamental or original trans- Vmitted wave is zero, and the potential of' the distortion or disturbing wave is not zero. Across .these points we have voltages corresponding to any disturbance present in the plate circuit which is n ot present in the grid circuit. We can now operate on the distortion without disturbing the fundamental or original vtransmitted `wave components.

For example, consider Fig. 4 and lFig'. 4A. Fig. 4 shows a feed-back amplifier system comprising three vacuum tubes. Ia, Ib, and Ic connected in tandem. Connected in series, across the grid and filament of tube` Ia, are a resistance I Sand the secondary winding of input transformer 4 which connects circuit 5 withv the amplifier. 'Ihe resistance I5 is suinciently great to make the impedance of this resistance and the secondary-toprimary impedance of the transformer in series substantially a pure resistance RT. The tube Ic is connected to theload or work'circuit Z, as

in the case of the tube I'of Fig. 3 and the tube Its value is Ic of Fig. 3E. As appears clearly from Fig. 4A, the impedance Z forms the output diagonal of the balanced Wheatstone bridge the ratio arms of which are Ro, KRO, KR and R. In the feedback diagonal of the bridge are a blocking condenser 9, a resistance RA and the resistance Rr in series with each other and in parallel with a circuit comprising a blocking condenser 9', resistance rc, a. blocking condenser I6, and the plate-to-filament space path resistance Rm of tube Ib in series. Preferably, the admittance of the space current supply path, through battery 6b and choke coil I1, which path is connected across R01, is negligibly small for the frequencies to be amplified. So also is the admittance of resistance I8 which is connected across the feedback diagonal of the bridge. Biasing potential from battery 8c is applied to the grid ,of tube Ic through resistances I8 and .r in series. The blocking condensers 9 and 9 prevent plate battery 6c from applying potential to the grids of tubes Ia and Ic, and prevent grid biasing batteries 8a and 8c from applying potentials to the grids of tubes Ia and Ic, respectively. A resistance I9 across circuit 5, and the primary-to-secondary impedance of transformer Lin parallel, approximately match the impedance of that circuit.

In the .circuit of Fig. 4 there will be no feed-` back of the fundamental or undistorted wave from the last tube Ic to the flrst tube Ia, if .r has, been given the proper value so that there is no fundamental or undistorted voltage across the feed-back diagonal of the bridge. It can be shown that thevalue obtained for in the above demonstrations holds when RA and RT and Ia and Ib are added to the circuit of Fig. 3C. However, the distortion introduced in the laststage will be reduced, as can be seen from the following consideration of Fig. 4A.

Let the distortion voltage acting in'the plate circuit of the last tube be o9 after its reduction caused by feedback in the last tube as explained in the case of the tube of Fig. 3 but before any reduction due to feed-back from the last tube to the first tube as about to be explained. There will be some distortion voltage Vo, impressed on the grid of the first tube as a result of the distortion produced in the last tube and Vo sets up a driving voltage MVO that may be .represented as a generator mVo in the plate-to-flament space path of the second tube. This impresses a voltage tVo on the grid of 4the last tube, which sets up'a driving distortion voltage ,antVn that may be represented as a generator lnot'io in the plateto-lament space path of the last'tube.

Since has been given such a value that the vcontribution of any voltage acting in series with or designating. the bracket in this expression ,32V

These specific values for Vo and p2 follow directly from the configuration of the specific circuit shown, but, though special to that partube Id (through which the signal componentsA ticular configuration, are given in order to present a concrete illustration of the significance of Vo and ,32.

:MeSH-Moffat) That is, the new driving distortion. voltage (ao-antw) is equal to the -old driving distortion voltage p09, multiplied by a factor'(1'pu2t).

Now if 'florist-:1, the ldistortion vanishes to zero. That is, if the product of the voltage amplifications and diminutions around the circuit is 1, and the phase shift is 180., the distortion voltage is balanced out. The amount of improvement in distortion in this circuit (over and above the improvement caused by feedback in merely the last' tube) depends on the accuracy with which the circuit elements areadjusted in such a way that any distortion component fed back from the plate-larnent'space path of the last stage to the K This operation of this circuit differs from that' of Fig. 3 and Fig. 3E, in that the improvement in crosstalk in those circuits is obtained by continued regeneration of the distortion voltage, instead of by the balancing operation described above. In those circuits, and in the circuit of Fig. 6 described hereinafter, it is neither necessary nor probable that the voltage fed around the circuit will be equal to that originally present. The operation just mentioned in the circuit of Fig. 4 may be considered asingle regeneration, with the voltage being fed around the circuit once, and. coming back in'opposite phase to that orig-l inally present.

The expressions continued regeneration and to express theabove noted difference in oper -1 tion of a circuit such as that of Fig. 4 from circuits such as those of Fig. 3 and Fig. 6 by stating that in Fig. 4 the amplified, isolated distortion components fed to the input circuit of the tube lc do not cause the magnitude of the isolated dist'ortion components (appearing across the input diagonal of the bridge) to be altered, whereas in Figs. 3 and 6 the distortion components fed back to the grid of the last tube cause reduction of the magnitude of the distortion components (thatV appear across the feedback diagonal of the bridge).

Fig. 5 shows a three-stage feed-back amplifier' system similar to that of Fig. 4, but modified of the first stage or tube la and amplifying the distortion components and the signal components together in that tube before passing them on to the grid of tube Ib, those isolated distortion components lare amplified separately from the signal, in an .amplier shown as comprising a single do not pass), and are then fed back to the grid of tube Ib. Thus, in the system-of Fig. 5 the amplification of the isolated distortion components can be`controlled independently oi the amplification of the signal components, and can,l for example, be made greater than the amplification of the signal components. The number of phase reversing amplifying stages (or other phase reversing means) in the path through which the distortion components are passed in their transmission from the feed-back diagonal of the bridge lto the grid of tube Ic should be even. Thus, in this path, the number of phase reversing means or stages (such for example as that comprising tube Ib) in which the signal components and the distortion components are amplified alike should be odd or even according to whether an odd oran even number of phase reversing means or stagesl (such as that comprising the tube Id) are used in which the signal is not amplified as the distortion components are.

In Fig. 5 the space current for tube lc is supplied from battery 6c through a choke coil 20 of negligibly low admittance for the frequencies of the'waves to be amplified, the current returning to battery 6c through resistance KRo. Condens- Aers Il, l2, I3 and i4 as well as condensers 9,

9' and I6, are stopping or blocking condensers which have negligibly low reactance-at the fre- -quencies to be amplied. If desired, the resistance KRO may be adjustable, as shown, to faciliresulting from variations in plate impedance of tube Ic caused for example by variations in the power supply voltages for the tube or by substitution of one tube for another. 'I'he impedance of the feed-backdiagonal f the bridge can-be adjustedA by a variable resistance 25 connected in parallel with a path comprising condenser 9', resistance :c (shown adjustable), and plate-tofilament space path resistance Roi of tube Ib in series. Also in parallel with the resistance 25 is a path, of negligibly low admittance at the frequencies of the waves to be amplified, extending through stopping condenser 9, input or coupling resistance RT for tube id, and grid biasing battery 8d for that tube, in series.- In, parallel with R01 is a path through choke coil ll and battery 6b in series, and also a path through grid biasing battery 8c and input or coupling resistance I8 for tube .ic. The two latter paths are of negligiblylow admittance at thefrequencies of the waves that are to be amplified. However, if desired, the magnitude of the combined resistance of these two paths and the space path of tube lb may be used as the magnitude R01 in the formulae above. The resistance RT in Fig. 5 corresponds to the resistance RT in Figs. 4 and 4A i and receives the voltage V0 indicated in Fig. 4A. In Fig.v 5 there is no resistance corresponding to the resistance RA in Figs. 4 and 4A; or in other Words the resistance RA is zero 'for Fig. 5. .The `batteryfb supplies space current for tube ld through choke coil 26. Tube Id feeds back to the grid of tube I b through condensers '3| and 32 and resistance 33 in series. justs the voltage thus fed to that grid; and these condensers adjust the phase of that voltage, the capacity of condenser 32 being variable and relatively large compared to that of condenser 3| to facilitate close or ne adjustment of the phase. As indicated above, the tube Id in Fig. 5 corresponds to the tube la of Figs. 4 and 4A as regards amplification of the distortion voltage Vu. This voltage sets up the driving distortion voltage ,nVo in thepath Roi, i. e., in the plate-tolament space path of tube lb in Fig. 5, just as explained above for the case of Figs. 4 and 4A. This impresses the voltage tVo on the grid of the last tube Ic, which sets up the driving distortion voltage nutVo in the plate-to-lament space path of tube Ic. As in the case of Fig. 4, the resist-v is zero, so that Vo is dependent solely on 09, the

original distortion voltage in the plate-to-iilament space path of tube Ic.

In an amplifier system substantially as shown in Fig. 5, if tube Ic in that gure be regarded as representing four tubes in parallel, the feed-back action reduced the energy contained in the second harmonic to 1/2,250,000 of its value Without the feed-back action, and reduced the energy of the third harmonic to 1/50,200 of its value without thel feed-back action. This result entailed no sacrifice of overall gain or ultimate level. Feed-back action of the type described for Fig. 3 tends to reduce the gain of the last stage (represented by tube Ic); Vbut the circuit of the type shown in Fig. 5 preferably is operated with this tendency to gain reduction in the stage comprising tube Ic not very pronounced, and with great reduction of distortion by the balancing operation of the type described for Fig. 4. The gain of the first two stages, comprising tubes la and lb, can be large, this portion of the amplifier serving as a voltageamplier for stepping up the voltage to the power stage represented by tube Ic.

harmonic is greater than the reduction of the third harmonic (as appears from the ratios given above), is primarily that although the second harmonic (and all even power harmonics) originated by distortion in the penultimate tube lb, and also all even power sum and difference frequency components or Waves so originated, are reduced by 'neutralizing or counteracting them (as described for the circuit of Fig. 4) with-the corresponding distortion waves produced by distortion in the last stage comprising tube lc, such. balancing out does not occur for odd order harmonics or other vdistortion arising from the presence of odd power terms in the amplifier' characteristic. The reasons for this difference will be apparent from the explanation given, for example, in U. S. patents toi-I. S. Read, 1,464,111, August 7, 1923 and H. Nyquist 1,570,770,"Janu ary 26, 1926, of the operation of tandem ampli-- fiers in reducing distortion wavesvoriginating in the amplifiers.

The preferable practice, in operation ofthe circuit of. Fig.5,is to adjust the value of a: so that the amplitude of the fundamental in the work circuit is the same for operation of the not shown, equal to the resistance of the platetolamentspace dischargepath in tube Id. To

make the distortion components balance out vin correcting means, as for example by condenser,

32 which can be adjusted to give the desired phase correction. A harmonic analyzer (not shown) can be connected across circuit 3 in order to tell when the best adjustment for 25 and 32 has been effected. With the circuit of Fig. 5 operated in the manner just described, although the third harmonic is not reduced below the value produced in the penultimate stage, the reduction o-.f the third harmonic originated by distortion in tube Ic is a very great improvement. Since the next to last stage (tube Ib) is operating at relatively low power level, and as a voltage amplifier working into a high impedance,

the modulation that it produces is Very small,

and has generally been considered negligible.

Fig. 6 shows a feed-back amplifier somewhat related to the amplifiers of Fig. 3 and Fig. 3E, and also to the ampliiiers of Figs. 4 and 5, yet having important differences from those four amplifiers as regards operation. The system of 6 comprises the tubes la, Ib and lc connected in tandem, and an auxiliary tube le for amplifying only distortion waves, as described.

hereinafter. Connected in series, across the grid and filament of tube la, are a resistance I5 and the secondary winding of input transformer V4 which connects circuit 5 with the amplifier. The resistance l5 is sufiiciently great to make the impedance of this resistance and the secondaryto-primary impedance of the transformer in serialI substantially pure resistance Rm.4 Other consider- The reason Why 'the reduction of the Second 5 ations entering into the determination of a suitable value for the resistance I 5 will be referred to hereinafter. The tube Ic is connected to the load or work `circuit Z, as in the caseA of the tube l of Fig. 3 and the tube Ic of Figs. 3, 3E, and 4. As in those four figures, the impedance Z forms the output or work circuit-diagonal of the bal-v anced Wheatstone bridge the ratio arms of. which are Ro, KRo, KR and R. In the feed-back diagonal of the bridge is a path comprising blocking condenser 9', resistance rr, and resistance Rm in series. In parallel with this path is a path oi' negligibly low admittance to waves of the frequencies to be amplified, which comprises blocking condenser 9, input or coupling resistance RT for tube le and grid biasing battery 8a in series. Battery 8a supplies grid biasing potential for tube I e as well as for tube la. Batteryl 6a supplies plate potential for tube le as well as for tube la. The resistance RT in Fig. 6 corresponds to the resistance RT in Figs. 4, 4A, and 5, and

receives the voltage V0y indicated in Fig. 4A. In

Fig. 6, as inFig; 5, there is no resistance correspending to the resistance RA in Figs. 4 and 4A; or in otherl wordsthe Jresistance RA is zero for Fig. 6. Tube lle feeds, in parallel with tube la,

' that Athe contribution of any voltage acting in series with Rai to the voltage V3 (see Fig. 4A)

across the input diagonal of the bridge is zero,l

so that Vov (which is the voltage across Rr) is the space. path of the last amplier as explained dependent solely on p09, the original distortion n Voltage in the plate-to-lamentspace path of tube Ic.A That is, f

' limpie0 x= Where p represents the amplification from a voltage across the grid of the auxiliary tube I e to a driving voltage in the plate-to-lament space.

of Fig. 6 is that, as in Fig. 5, the funda-mental or original transmitted wave components are not regenerated through the auxiliary tube, and c on-v sequently the gain reduction that such regeneration would entail if it occurred is obviated. Distortion `waves are regenerated (negatively), in a manner analogous to that in which they are regenerated (negatively) in Figs. 3 and 3E, through tubes le, Ib, and Ic. Thus, there results a reduction of distortion, the magnitude of the reduction depending on a factor l-l-pr', where a represents the voltage amplification, and el the voltage diminution, around the circuit through tubes le, Ib and Ic or through the path comprising the auxiliary amplifier and that portion of the signal amplifier forming with the auxiliary amplier a regeneration circuit for distortion waves. (l' here corresponds, in connection with Fig. 6, to i and ,'32 referred to above in connection with Figs. 3 and 4, respectively.)- phase reversing means, as for example, amplifying stages, in this path should be odd, but the number of amplifying stages in it may be as great as desired: so the reduction of distortion -can be as great as is necessary. Moreover, as long as the number of phase reversing means in this path is maintained od'd, the auxiliary ampli-` er may have any desired number of stages, the number-of stages of the signalamplier used 'in Y this path being then made any desired number which will make the total number of phase re- Versing means in this path odd. For example, tube le may be replaced by three tubes in tandem. Inl cases where, for the desired degree of reduction of distortion, this path requires a greater number of stages than vwould be available for it in the signal amplifier as designed without reference to suppression 'of distortion by feedback action, it will ordinarily be advisable to use a plurality of stages in the auxiliary amplier rather than to increase the number of stages in the signal amplifier; for ordinarily the operating requirements for the auxiliary amplifier, with respect to load capacity and constancy of power supply voltages, impedance and gainfor exam- Aple, are much less severe than those for the signal amplifier. Since the only load carried by lthe auxiliary amplifier is the light load of the distortion waves, it originates 'very little distortion. In the system of Fig. 6, as well as in that of Fig'. 3, the feed-back action increases load carrying capacity, decreases distortion, and increases stability of gain with tube and power changes.

In Fig. 4, neither distortion components nor fundamental or original transmitted wave components 'areregene'rated, except in the last 'Ihe number of tube. However, thev distortion components are fed back around the circuit once. The reduction of distortion in the system of Fig. 4 depends primarily on how well the amplitude and voltage of the two opposing voltage waves are adjusted. The overall gain of .the 'circuitneed not be reduced, although the gain of the last tube is reduced somewhat.

In Fig. 6, in the auxiliary tube or tubes used to amplify the distortion, only the distortion components are regenerated, and not the fundamental or original transmitted wave components. Thus, .the improvement with respectto distortion, load capacity'and gain stability does not depend upon sacrifice of the gain of the amplifier. Both the distortion components and the fundamental or original transmitted wave components are regenerated (negatively) through the path comprising the signal transmitting tubes I a, Ib and lc; but the consequent reduction of gain can be umade small since not this. regeneration but the regeneration of the distortion waves through the path includingy theauxiliary amplifier, is the regeneration preferably relied upon to produce the` principal reduction of distortion. In order to obviate large gain reduction caused by regeneration through tubes la, lb and lc, the ratio Roi/(Roi-l-x) is preferably made small. However, as explained above, I5 should be sulfi- .ciently large for proper phase control. Moreover,

R01 is preferably small. For` if Roi/(Roi-l-) is to be small, R01 should be srn'all unless :c can be large; and the larger a;v is made, the smaller becomes fr, since :c=(R-}-Ro) /p.. It is advantageous to make R large both because increase of R tends to increase e and because increase of R tends to increase the stability of operation of the system, especially as regards gain and distortion elimination as affected by variation in plate and filament voltages and other circuit variables.

Each of the systems shown in Figs. 3, 4 and 6 is typical of a wide Variety of possible circuits.

The principles of operation described for any,

one or two or all three of these three types of circuits are applicable in general to devicescapable of amplifying waves, for improvement of their operation. These principles are of very broad and general application. Their application is by no means limited to operation intended to be mere amplification. The theory of these systems has been checked by careful tests of physical embodiments of the systems.' Each of these systems reduces both odd order and even order distortion components at the same time,

' and can stabilize gain and afford high load capacity.

One difference between Fig. 4 on the one han and Figs. 3 and 6 on the other hand, lies in the relative seriousnessof unavoidable'phase shifts in the amplifier, Since the effectiveness of Fig. 4 depends on the production of two voltage waves of equal amplitude, and opposite sign, a good balance requires that the phase difference be very close to 180, and that the gain' of the circuit change very little after a balance is once attained. However, in Figs. 3 and 6, the

improvement depends on the factor I indicating a factor such as ,81 or ,81' v(or z) mengain to change by 3 db so that p=7+:0, then i an improvement of 18.0 db. A similar change in circuit to form thatof Fig. 7. A second bridge' circuit is formed, with a ratio arm constituted by the network that faces the output diagonal of the first bridge. In this arm, therefore, is

a voltageproportional to the residue of distortion remaining after the first balancing. 'I'he fundamental ororiginal transmitted wave components are also present in this arm. The other three ratio arms-of the second bridge are KRo, KR, and R', corresponding respectively to the ratio arms KRa, KR, and R of the rst bridge. The output or work circuit diagonal of the second bridge is the condenser and the primaryto-secondary impedance of amplier output transformer 2 in series. The resistance :r corresponds in function tovresistance x, and is of such magnitude that the voltage of the fundamental or original transmitted wave components across R01 and :c in series (i. e., across the feedback diagonal of the second bridge) is zero. Thus the primary Winding of a transformer 35, which is connected across the feed-back diagonal of the second bridge, receives only a Voltage proportional to the residue of distortion just mentioned. This voltage is amplified in amplifier I'd andthe amplified voltage is fed through resistance 33 and condenser 3|' to the grid or input circuit of tube Ib. It is apparent that the residue of distortionjust mentioned is isolated from the fundamental components and fed back in the same fashion as the first process. the distortion is again improved by approximately the same ratio as before. In balancing circuits which have heretofore been used for reducing distortion (such as the Colpitts push-pull circuit), only ,one improvement can be achieved, and that only for odd order or even order distortion components and not for both odd order and even ordercomponents at the same time;

whereas the improvement obtained with thecirpedance RT of transformer 35 is connected' Vacross the feed-back diagonal of the second bridge as the impedance RTis connected across the feed-back diagonal of the first bridge.-

'I'he circuit of Fig. 6 can be made cumulative in Thus Ian improvement of 20.8 db. `If we assume the its action by extending it to form the circuit of.

. or original transmitted wave components are also present in this arm. The other three ratio arms of the second bridge are KRo, KR, and R', respectively. The output diagonal of the second bridge is thel primary-to-secondary im#- pedance of amplifier output transformer 2. The resistance .'c corresponds in function to. the resistance a', and is of such magnitude that the voltage of the fundamental or original transmitted wavecomponents across Roi and in series (Lie. across the feed-back diagonal of the second bridge) is zero.v Thus, the tube l'e, which has its input or coupling resistance RT connected across the input corners of the second bridge diagonally opposite each other, receives only a voltage proportional to the residue of distortion just mentioned. This voltage is amplified in amplifier |e and the amplified voltage is fed to the grid or input circuit of tube b. It is apparent that the residue .of distortion just mentioned is isolated from the fundamental components and fed back in the same fashion as the first process. Thus, the distortion is againl improved by approximately the same ratio as before. As explained in connection with Fig. 'A7, as many 4bridges as desired may be connected in tandem in a circuit such as that of Fig. 8.

Fig. 9 shows an amplifier circuit in which distortion waves are isolated and fed back in a manner similar to that described for the circuit of Fig. 6, but instead of an auxiliary' tube for amplifying theisolated distortion waves an auxiliary grid or space discharge control electrode 4| in signal amplifying tube |'c is employed, the isolated distortion waves obtainedv across and Roi in series (i. e. across the feed-back diagonal of the Wheatstone bridge) being impressed on grid 40 through the blockingcondenser 9 and ampli-l The distortion waves are iso,

components is zero. A battery 8c supplies bias-V ing potential to the grid 4| through a choke coil 42 which has negligibly low admittance at the ordinarily a positive potential as is usually the case for the auxiliary or second grid of a four- Aelectrode tube used to amplify two waves impressed on -its main and auxiliary grids, respectively.

Fig. 10 shows a feed-back amplifier especially suitable for use in amplifying a plurality of mes-l sages simultaneously, as for example an implifier in a line over which multiplex carrier telephone transmission is effected. This amplifier operates to reduce distortion inv the-general manner ex" plained in connection with Fig. 6. However, the systemyof Fig., l-'comprises five4 stages of signal amplifying tubes in tandem and two amplifier stages in the auxiliary amplifier for amplifying distortion waves only. The .,rst, second, third and fourth stages of signal amplifying tubes comprise tubesllil, Ia, Ib, and I'b, respectively. The

from aioaero t fifth stage comprises tubes ic1`and les in parallel with each other and tubes Ica and ,fc4 in parallel with each other, the pair Ici and -lcz being in with each other andin series with'the filaments of tubes l'b, lez and ici. Filament heating current' is supplied from battery 1' through choke coil 52' to a path extending through the filament of tube 5I and a resistance 53 in parallel, thence through the filaments of tubes la and le in parallel, and thence through the filaments of tubes Ica, and fc4 in series.`

Biasing voltage, obtained as the voltage drop across the filamentsof tubes la and l e and tube lcs, is applied to the l secondary Winding of input transformer 4 which couples circuit 5 to tube 5I. Biasing voltage, ob-

tained as the voltage drop across the filaments of tubes [c: and fc4, is applied to the gridof tube la through the secondary Winding of an interstage transformer 54 through which tube 5l feeds tube la, and is applied to the grid. of tube 'le through resistance RT. Biasing voltage, obtained as the voltage-drop across the lamentsoof tubes Ib" and Icz, is applied to the grid of tube` Ibv through lnputor coupling resistance 5B, and is applied `to the grid of tube I'ethrough the secondary winding of transformer `51 through which tube Ic feeds tube I'e. ,Across coil 52 and battery 1 is connected a resistance 55, and across coil 52 and battery 1 .is connected a resistance 55. The positive poles of grid biasing batteries 8 and 8' areadjustably connected to resistances 55 and 55', respectively. Biasing potential from a pdint on battery a is applied to the gridof tube Ib through the secondary windingof an interev -stage transformer 64 through which'tube ib feeds tube Ib.l B iasing potential from a point on battery 8 is applied to the grid of tube Ici through a secondary coil 65- of a transformer 65 through which tube I'b feeds tubes Ici, Icz, lcs and Ic4. Biasing potential from a point on battery 8 is applied to the grid o-f tube lcz through a secondary coil 51 of the transformer 65. Biasing potentials from points on battery 8' are applied tothe grids ofA tubes Les -and |04 through secondarycoils and 69, respectively, of the transformer 65.- y'

Plate potential'for tubes 5|, Iaand le is supplied from plate battery 6 through the'primary winding of transformer 54, the primary winding of. transformer l5,1, respectively. Plate potential for tubes Ib' and `l'e is supplied from` this battery through the primary l winding of vtransformer 64. Plate potential for tube I'b is supplied from this battery-through the primary winding of 'transformer B5.`

Plate potential for tubes Ici and Ici is supplied' plate battery '6c by a circuit extending through a choke coil 12, the upper half of primary winding of transformer 2, and thence through a .path having .a branch KRo in parallel with a branch comprising a resistance KR and the upper vhalf of the primary winding of a transformer 13.

Plate potential for tubes lcs and Ic4 is supplied from plate batteryy l6c by a circuit extending vthrough a choke coil 12', the lower half of primary windingA of transformer 2, and thence through a, path having a branch KRo 'in parallel with a branch comprising a resistance and the lower grid of tube 5l through the a choke coil'.1| and' cuit of tube Vb..

half of the primary winding of the transformer 13. y

The impedance of the plate-to-filament space path ofpeach of the tubes Ici, lcz, lcs and iciA is 2R. Thus, the impedance of the space paths of tubes Ici and Ilczv in parallel is R0. This impedanoe Ro forms one-of the ratio arms of a network which can be regarded as a balanced Wheats tone bridge, the other three ratio. arms of which are R, KR and KRD, and one diagonal of which is the upper half or coil of the primary Winding of transformer 13. This diagonal'is the feed-back diagonal of this bridge.

The impedance of the combined space paths of tubes I es and fc4 in parallel is Ru. This impedance Reforms one of the ratio arms of a network which c-an be regarded as a. balanced Wheatstone bridge, the other three ratio arms of which are R, KR and KRO, and one diagonal of which is the lower half or coil of the primary winding of transformer 13. This diagonal is the feedback diagonal of this bridge. As can be seen from the symmetry of the two bridge circuits in Fig. 10, blocking condenser il as well as the junction of the two resistances R is at ground potential for A. C.v Consequently, the upper and lower coils of the primary winding of transformer 2 can be regarded as diagonals- (output diagonals), respectively, of the bridges which have the upper and lowercoils of the primary winding of transformer 13 as their feed-back diagonals.'

The designation of the plate impedance of each oftubes Ici, Icz, les and Ic4 as 2Ro is not to indicate that these impedances are higher han those of tubes described above as having late impedance Ro, but is to facilitate comparison of the bridge circuits of Fig. with Athose of other figures of the drawings. 1'

The resistance of the plate-to-iilament space path of tube la is R01. A path comprising this impedance and resistance :c in series is connected across the secondary winding of transformer 13, through' blocking condenser 9'. In parallel with this path isa path of negligibly low admittance to waves of the frequencies to be amplied, which comprises blocking condenser 9 and input or coupling resistance RT for tube le in series. The shunt across R01 through choke coil 1l and batquencies ofthe waves to be amplified. The resistance RT in Fig. 10 corresponds to the resistance RT in Fig. 6, and receivesthe voltage' V0 indicated in Fig. 4A from the secondary wind.-

ing oftransformer '13.` The auxiliary amplifier comprising tubes le and le lin tandem feeds. in parallel with tube Ib, into the grid or input cir- As in the case of the resistance a: in Fig. 6,

the resistance :r in Fig. 110 is given such a value that the. contribution of any voltage acting inseries with R01 to the voltage V3 (see Fig. 4A)

'across R01 and :r in series, is zero, so that Vo (which isthe voltage across RT) is dependent solely onpoe, the original distortion voltage in the plate-to-lament space path of each of the y tubes Ici, ice, lcs and Ic4. Thus, as explained in connection with Fig. 6, the `value of n: is such that the fundamental or original transmitted wave components have zero voltage across'the at least, the auxiliary amplifier comprising'tubes le and le, asin the case of the auxiliary amplifler tube' Ie in Fig. 6, amplies only distortion grid and .filament of tube le. Thus, theoretically they are regenerated in Fig. 6, through tubes le, Ie, I'b and the push-pull stage comprising tubes Ici, Icz, Ic: and Ici. Thus, there results from the feedback action a reduction of the dis. tortion produced in the tubes of the last stage, as in the oase of Fig. 6, and also, asin the case of that figure, increase of load capacity, and increase of stability of gain with tube and power changes. In Fig. 10, as in Fig. 6, the improvement in these respects does not depend upon sacrice of the gain of the amplifier.

Circuit 3 is fedA from the amplifier through the transformer 2. The voltage across the path'consisting of the two halves or coils of the primary winding of the transformer and blocking condenser in series, is the sum of that across R and KR in the Wheatstone bridge which has the space path of tubes |c1 andy Ica as one of its ratio arms and that across R. and KR in the Wheatstone bridge which has the space path of tubes Ica and Ici as one of its ratio arms. In each of these bridges, with respect to A. C. the

- output diagonal or work circuit diagonal can be regarded as terminating at the cathode of the discharge path included in a ratio arm of the bridge, the feed-back diagonal terminating at the anode of the path; whereas in the bridge in the other figures, the feed-back diagonal terminates at the cathode and the output or work circuit diagonal terminates at the anode.

As isordinarily the case in output transformers v cumulative effect of the output of fundamental or original transmitted wave from the tubes which feed these coils. Similarly, the resistance RT can receive the cumulative effect of the output of fundamental or original transmitted wave and odd harmonics from the tubes Ici, Ica, Ica and |04.

' RT are fed back as described above in connec- -tion with Fig. 6, to reduce those components als appearing in the work circuit 3.

Fig. 11 is a set of curves plotted from observed data, showing the output of second and third harmonics as functions of output 'of the fundamental or original transmitted current, for a system of the type of that shown in Fig. 5. The curve for the second harmonic taken with regeneration shows that with an output of fundamental up to 30 milliamperes into an impedance of 600 ohms, the power level of the output of second harmonic is 90 decibels below .the power'I level of the output of fundamental. This means that the fundamental power is about 900,000,000 times as great as the powerl of the second harmonic, and that the current ratio of fundamental to second harmonic is about 30,000. The curve for the second harmonic taken without feedback shows that up to 30 milliamperes output of fundamental the output of second harmonic is only about 30 db. lower than the output offundamental (i. e., the power output of fundamental 'is only about 900 times as great as the power 'output of second harmonic, instead of 900,000,000 times aswhen feedback is employed). For current outputs greater than 30 milliamperes of fundamental, the curve for the second harmonic for operation with feedback is still well above the curve for the second harmonic for operation without feedback. Likewise, the curves for the third harmonic tak`en with and without feedback show great reduction of the ratio of that harmonic to the fundamental, as a resultof the feedback."

The distortion components` fed backto' the plate of tube Id and connected instead to ground through a passive impedance (not shown) equal to the resistance of the plate-to-filament space discharge path in tube Id.

Fig. 12 is a set of curves plotted from observed data, showing the overall gain as a function of current output into a 600 ohm resistance, for the fundamental, in a specific system of the type of that shown in Fig.A 5. Below about 30 milliamperes of output current the solid line curve, which is for operation with feedback, substantially coincides with the dotted line curve, which is for operation without feedback. This is in marked contrast to the gain-load curves of Fig. 3D .for the circuit of Fig. 3, inasmuch as the feedback in the latter circuit lowers the gain. In Fig. 12

the solid line curve lies well above the dotted line curve, for outputs considerably greater than thirty or forty milliamperes, thusy showing great gain stabilization effected iby the feedback, this stabilization being effected 'without gain reduction corresponding to such reduction indicated by Fig. 3D for the circuit of Fig. 3.

It is desired to emphasize the fact that the invention increases the load carrying capacity of electric. space discharge tubes (l) not only by attaining an increase in load capacity of very great limportance byy suppression of distortion components of frequencies other thanthe fundamental frequencies and thereby permitting the tubesv to operate over a larger range of their grid-voltage plate-current characteristics but also (2) by attaining a second increase of very great importancev in lthe load capacity by feedback of fundamental waves in such a way as to control gain in a desired manner, as for example, to prevent undesired loweringv of gain, for the fundamental waves. y

In connection with this latter increase, it should be noted that in each of the amplifyingvsystems .described herein the invention provides means for correcting for distortion caused by improper .degree of amplification of fundamental waves,

as for example caused by amplification of a,fun damental wave of a given frequency different amounts for different input amplitudes, or as for example caused by amplification of two waves of respectively different fundamental frequencies, different amounts, respectively. If in Fig. 6, for example, a wave of a given fundamental fre- K quency is amplified in any or all of tubes la, Ib

and Ic (or the circuits associated with the tube or tubes) toa degree less than, say, the normal amplification-for the tube or vtubes (and the as-l sociated circuits) then for that frequency the feed-back voltage, or regenerated voltage across the feed-back diagonal of the bridge tends to be lower. than normal, i. e., less thanl the fundamental which is applied there from circuit i through Roi and z. As a result, 'the tendency toward lower than normal gain of thesystem for the fundamental wave of the given frequency is checked. Similarly, if the given frequency is amplified to a degree greater, instead of less, than normal in tubes la, lb and Ip'. then for that 75 .waves to the input circuit oi said device in auch frequency the feed-back voltage tends to be high er than the voltage of that frequency which is applied across the feed-back diagonal by circuit through R01 and z; and as a resultthetendency toward higher than .normal gain of lthe system for the fundamental wave of the given frequency 7is checked. 'I'he system compensates `ses sistances.

for too low or too high gain Afor fundamental waves, at'the same time that it suppresses components of frequencies other than fundamental frequencies.

Forthe sake of simpl'lcitythe-invention has been explained above with reference especially to pure resistance impedances where impedances lhave been described as external or ratio .arms of Wheatstone bridges, or as input diagonals of the bridges. However, the invention is net limited to the case in which these impedances are re- They, aswell as the load, may be impedances of any character, (proper provision being made, of course, for the necessary supply o! steady potential to theA plates and grids of the tubes). This is Aindicaied'by Figs. 3F, 4B and 6A, which are like Figs. 3, 4 and 6 respectively, except that Zo, KZ, KZz. Z. Zr, Zon'ZA and Z'r replace Ro, 'KRm KR,.R, .1:,.Rci, RA and Rr, re spectively. 'These replacements may likewise be made in the mathematical formulae and expressions above. Moreover, as indicated in the'above description of Fig. 10, and as further indicated by Fig-9A, in any ofthe figures .of the drawings the bridge arms R and KRD. (or Z and KZu),l may 'oe interchanged in their positions in the bridge. In any of the gures; of the drawings the imped ance Zo includes the tube internal plate-to-filament capacity. Where Rn has been treated as constituting one arm of the bridge, theplate-illament capacity-r` is "so small that its reactance at exclusion of waves produced without 'frequency change by the applied waves, and means for impressing the derived waves on the input'side of said apparatus.

2. In combination, wave translating apparatus,

' means for applying lto, said ,apparatus waves producing modulation in said apparatus, wave balancing means for derivingjrom the modulation' components, waves including odd order modulation components to the substantial exclusion oi' waves produced without frequency change by the applied waves, and means for impressing the def rived waves on the input side of said apparatus in such phase as to reduce'the magnitude of the4 modulation components produced in said apparatus.

3. A system comprising an electric space discharge device having an anode, acathode and a.

discharge control element, means for isolating y first mentioned waves, amplifying means for pr`o` ducing -from said isolated waves amplined Waves of the same frequency and phase as said isolated waves, and means for feeding said amplidedv sense as to reduce the intensity of the -rst men tioned waves.

4. In combination, an electric space discharge device having an anode, a cathode and a dis'- charge control element, means for isolating waves produced by said device in response to waves of frequency diil'erent from the frequency'of the first 'mentioned waves, a Wheatstone bridge included in said means and having three of its arms passive impedances, and means connecting the space dischargek path between said anode and said cathode in the remaining arm of said bridge.

5. In combination, an electric space discharge device having an anode, a cathode and a dischargecontrol element, means for isolating waves produced by said device in response to waves of frequency different from the frequency of the first mentioned waves, a Wheatstone bridge in cathode in the remaining arm of said bridge. and

means for supplying the second mentioned waves -in adiagonal of said bridge. 6. The method of operating wave translating apparatus which comprises applying to said ap paratus waves producing modulation in said apparatus, isolating modulation products, supply,- ingtheisolated 4products to the input circuit of the apparatus to alter the magnitude of the modulation products, deriving from'the output waves of said apparatus waves of frequencies of the modulation products but exclusive of waves produced without frequency change by the applied waves, and impressing the derived waves on the input side of -said apparatus to further alter the magnitude'of the modulation products.

7. In combination, wavey translating and dis-` ftorting apparatus, means for applying' to said apparatus waves producing in said apparatus vdistortion components including odd order modulation', wave balancing and isolating means for deriving distortion components includingv wavesof the frequency of said odd order modulation componentsfrom distortion components produced in said apparatus, and means for so impressing the derived waves on said apparatus as to alter the intensity of the derived waves.

' 8. In combination, wave translating apparatus.

means for applying tosaid apparatus waves'pro-A ducing in said apparatus waves including odd and even order products omodulation, wave ancing and isolating means for deriving. from the produced waves, waves of the frequencies of said odd -and even .order modulationproducts to the substantialexcluslon o'wavcs produced without frequency change by the applied waves, and means for so impressing the derived waves on said apparatus as to alter-the intensity of the derived waves.

9.'The method oi operating wave translating apparatus which comprises applying to the in put side oi the apparatus waves which produce modulation in the apparatus, balancing waves fromthe output side of the apparatus againstl the applied waves to isolate modulation products,

amplifying the i isolated modulation' pructs alone, and impressing the amplled products onld. In combination,- wave translating 1w rav tus comprising an electric space discharge @uw having an anode, a cathode and two discharge v -control elements, means for supplying to one of said controlelements waves producing` modulation in said apparatus, and means for isolating .modulation products and impressing themen said other control element.

l1. The method of operating'wave translating apparatus which comprises applying to said apparatus waves producing modulation insaid apparatus, isolating modulation products and lmpressing them on the inputside of said apparatus to alter the magnitude o f the isolated products and of the modulation products, deriving from the output waves of said apparatus waves of frequencies of the modulation products but exclusive of waves produced without frequency change by the applied waves, and impressing the derived `waves on the input side of said apparatus.

12.A In a. signal wave repeater having input and output circuits, means for reducing distortion-r comprising means coupling the output and input circuits for odd and even order distortion componente but'not for the signal components.

13. In combination, a plurality of electric space discharge devices connected in cascade relation. connections for producing negative feed-back of waves from the output circuit of the last one of said devices tothe input circuit of that device,

.and connections for feeding from the first mentioned connections to the input circuit of the rst one of said devices distortion components generated in said last one of said devices, to the ex-v clusion of waves originally transmitted through the preceding ones of said devices.

14. The method which comprises vso operating upon fundamental waves as'to produce a'. resulting wave containing fundamental components of the frequencies of said fundamental waves `and modulation products different from said fundamental components, isolating said modulation products from said fundamental components by.

balancing said fundamental waves exclusive of ,other waves against said fundamental compo'- ,nents in said resulting wave,'and regenerating said modulation products.

15. 'The method of operating an cuit which comprises transmitting to said circuit 'fundamental waves which produce ifi 'the circuit a. resulting wave that contains fundamental components of the frequencies of said fundamental waves and distortion products different from said fundamental components, isolating said distortion products from said fundamental componentsl by balancing said fundamental waves exclusive of other waves against said fundamental components in said resulting wave, and so regenerating salti distortion products in said circuit as to reduce them.

1 6. A circuit comprising a wave translating deyvice, means for transmitting fundamental-waves amplifier circircuit as to control the transmitted against waves' transmitted through said device, said path having such trnsmisslon eillciency and phase'shift that the fundamental waves transmitted therethrough, neutralize the fundamentaicomponent of the opposedy distorted waves from said device and thereby yield the distortion components without fundamental waves', and means forcauslng these isolated distortion componentsvto beso regenerated in said amplitude ofthe distortion oomponents.". :1 l

18. A circuit comprising a vacuum tube device, means fortransmitting to said 'device fundamental waves which produce-distortioncomponents in said device, 'aV lWave transmission path 'for transmitting the fundamental waves/substantially ,without -distortionand opposing the waves so transmitted against lwaves transmitted through said device, said path having such trans'- 4 the frequencies of said fundamental waves and distortion products different f from said fun'da- .mental components, isolating said distortion products from said fundamental components by balancing said fundamental waves exclusive of other waves against said fundamental components in said resulting wave. amplifying said isolated distortion components in their isolated to said device which'produce in said device a resulting wave containing fundamental components that. have the same frequencies as said fundamental waves and distortion products differing from said fundamental components, means for so opposing said fundamental waves exclusive of other waves to said fundamental components in said resulting wave as -to isolate said distortion products, and means for regenerating in said circuit saidv distortion products only.

17. A circuit comprising a wave translating device, means fr transmitting to said device fundamental waves which produce distortion compoy'nents in said device, a wave transmission' path for transmitting the fundamental waves substantially -fv'frithout distortion and opposing the waves so state, and thereafter amplifying them withsaid fundamental waves to control the effective magnitude of said distortion products in said resulting wave. e. A

20. A wave translating system comprising a vacuum tube device having a grid, a' clrcuit fed from said device, means for transmitting fundamental waves to said grid, means forderiving from a portion of said clrcuit a resulting wave* containing fundamental components that .have

the same frequencies as said 'fundamentalwaves and distortion products differing from said fundamental components, means for so opposing said fundamental waves exclusive of other waves to said fundamental components in-said derived Avvavc asto isolate said distortion' products, and

means for. so feeding said distortion products backto auch a portion of said system anterior to said portion of said circuit 'as to cause the amplitude of said distortion products to be reduced by repeated reamplincation in a portion of said system anterior to said portion of said circuit but exclusive of said grid.-

21. A vacuum tube having two electrically separate grids. means for transmitting to one of said grids fundamental waves which produce in said device a resulting wave containing fundamental components that have the'same frequencies-as said fundamental wavesand incidental distor' tion products of frequencies different from their respective fundamental components, means for so opposing said fundamental'waves exclusive of other waves to said fundamental components in said' resulting wave as'to isolate said distortion products.V and means vfor feeding said isolated distortion products to said other grid-in such phase as to reduce their magnitude by rev peatedly regenerating them in said device.

22.v In a signal amplier having an input and an output circuit, saidamplier having a nonlinear relation between output and input waves whereby the amplifier tends to produce distortion in the form of signal modulation components along with the ampliiied signal, means for reducing the distortion so produced comprisingv a circuit for feeding back odd order modulation components to the substantial exclusion of signal components from the output circuit to the input circuit opposing the tendency of' said ampliiier to produce said distortion.

23. In a signal amplifier having an input and an output circuit, said amplifier having a nonlinear relation between output and input waves wherebyA the vamplifier tends tov produce distortion inthe form of signal modulation components along with the amplified signal, means for re- 'ducing the distortion so produced comprising a circuit for feeding back odd and even order modulation components to the substantial exclusion of signal components from the output circuit to the input circuit opposing the tendency of 'said amplifier to produce said distortion.

24. In a signaling system', a line for transmitting waves of a broadband of frequencies, said line divided into sections, an amplifying repeater having an input circuit coupled to an incoming line section and 'an output circuit coupled to an outgoing line section, said repeater having a nonlinear relation between output currents and induceV components of' new frequencies by interaction between diierent input frequency components within said -1 broad band, and a .circuit lfeeding back some o! the output voltages, includ- 40 ing odd and even order components of said new frequencies tothe substantial exclusion of signall components, from the output circuit to theinput circuit in opposingrelation whereby the ampli- :tude of'the'new frequencies appearing in the outgoing-line section is reduced. 25. A' signal wave'repeater comprising an input and an output circuit, means to impress signal waves on said input circuit to be repeated, an.

outgoing circuit for the repeated waves connected between two points inv said output circuit between wl'iicha ydierence of potential of the signaling frequency exists, said output circuit. hav- -i'ng a branch across which a difference of potential corresponding substantially only to odd and even order productsV ofk modulation-between the impressed .signals is developed, and means for' reducing signal distortion insaid repeater comfprising acircuit connection between said branch andthe input circuit for impressingv said odd' and even .order modulationproducts on said input circuit in such phase as to reduce production of said modulation components in said output.

26. In an amplifier circuit, a space discharge device having. an-input and an output, a source of waves to beamplied applied to the input circuit of said device', a load circuitconnected to said output in series with an external impedance, a branchcircuit .connected to said-device, said load circuit and said'external impedance, across which a diiference of potential is developed, representing odd and -even order modulation prodv Vmits of said applied wavesto be amplifledto the substantial exclusion of the waves to be amplifled, andmeans for reducing the amount' of mod- Put voltages whereby the repeater tends t0 PrO- .fying means for producing from said isolate said device in such sense as to reduce the intensimanon produced in said amplifier circuit coniprising a circuit for applying to the input oi said device a portion of the voltagedeveloped in said branch, in a phase to reduce production of modulation in said amplifier circuit.

27. In combination, wave translating appa- 5 ratus, means for applying to said apparatus waves producing modulation in s aid apparatus, wave balancing and isolating means for deriving, from the -modulation components, waves including odd order and even order modulation com- 10 ponents to the substantial exclusion of waves i produced without frequency change by the applied waves, and means for impressing the derived waves on the input side of said apparatus.

`magnitude of lthe modulation components pro- 25 duced in said apparatus. y

29.5. system comprising an electric space discharge device havingan anode, a cathode and a discharge control element, means for isolating waves including odd order and even order moduvlation products produced by said device in response to application to the input circuit of said device of waves of frequencydiiferent from the frequency of the rst mentioned waves, ampli- 35 d waves amplified waves of the same frequency and phase as said isolated waves, and means for feeding said amplified waves vto the input circuit of ty of the iirst mentioned waves. 40 30. lAn active transducer; a feedback path therefor for' feeding back in said transducer distortion components produced from fundamental componentsby saidtransducer to the substantial Vexclusion of the fundamental components, 45

and a second feedback path conjugate to the rst mentioned feedbackpath, for feeding waves back in said transducer.

31. An amplifier and two coniugate paths each feeding back in said amplier distortion compo- 50 nents produced from fundamental components by said amplifier to the substantial exclusion of 'the' isolate said distortion products, and means for 65 feeding said isolated distortion products to said other grid.

33. A vacuum tube system comprising a vacv uum tubev having two electrically separate grids.

means for transmitting to one of -said grids funl0 damentalV waves which produce in said-system a resulting wavepcontainingfundamental components that' have the same'frequencies as said fundamental waves and distortion products of irquency different from said fundamental com-'15 f ponents, and means for so feeding Said distortion products tosaid other grid as to reduce the distortion products in said resulting wave.

34. Themethod whichcomprises so operating upon fundamental waves as to produce a resulty ldamental waves to said device which produce therein a resulting wave containing fundamental components that. have the same frequencies as vsaid fundamental waves and distortion products differing from said fundamental components,

g means for so opposing said. fundamental waves exclusive of other waves to said fundamental components in said resulting wave as to isolate said distortion products, and `means for so regenerating said distortion products in said device that they reappear at their place of' originin reversed phase. o

36. A circuit 'comprisinga wave translating device, means for transmitting to said device fundamental waves which produce distortion components insaid device, a wave,.tran smission path for transmitting the fundamental waves substantially without distortion and opposing the waves so transmitted against ,waves transmitted through said device, said path having such transmission efficiency and phase shift that the fundamental waves transmitted therethrough neutralize the fundamental component of the opposed distorted waves from said device and therebyyield the distortion componentswithout fundamental waves,

and means for causing these isolated distortion components to be so regenerated that they reappear at their place cf origin in reversed phase.v

37. A system comprising a plurality of stages -of electric space vdischarge devices, means for isolating distortion components produced in signaling waves by their transmission through said devices from signaling components of the waves,

-said means including paths for balancing waves on the input side of the rst device against signaling components of equal amplitude but opposite phase in waves from'the'output side of the last device, and means for feeding distortion waves resulting from said balancing action through said devices.

38. A systemcomprising a plurality of stages of electric space discharge devices, means for iso.

lating distortion components produced in signaling waves by their transmission through said devices from signaling components of the waves, said meansA including paths forbalancing waves 'on the input side of the .rst' device against signaling components of equal amplitude but opposite phase inwaves from the output side ofthe last device, means for feeding distortion waves-resulting from said balancing action through said f devices, and means for compensating for phase tends to produce in' the latter waves.

of electric space discharge devices, means for isolating distortion components'produced in signal-- shift which passage of waves through said stages 39. A system comprisinga plurality of stages ing waves by their transmission through said dean'oaevo vices from signaling components of the waves, said means including paths for balancing waves on the input side of the first device against signaling components of equal amplitude but opposite phase in waves from the output side of the 'last device, and means for amplifying only distortion waves resulting from said balancing ac- -tion and feeding the amplified waves through `'said devices.

40. A signal receiving system comprising a multiplicity of amplication stages, and means coupling a portion of one amplication stage with a portion of a preceding amplification stage for impressing energy thereon in 180 phase displacement with respect to incoming signaling energy in said preceding amplication stage for regulating the amount of energy in said signal receiving system, and voltage balancing means for opposing undesired transmission of voltage from said one stage to said preceding stage through said coupling.

41. In an electrical amplifying system, a ther- 4 mionic vacuum tube, aninput impedance for said -tain proportion offthe output energy of said first tube 42: In an electrical amplifying system, a plurality ofelectrical amplifiers, means for impress-t ing upon said ampliers certain portions of a signal to be amplified, means for combining the output -of said amplifiers in a common output circuit, means for impressing on the input of one of said amplifiers a portion of the output of another ofv said amplifiers, means for reversing the phase of the amplified signal currents, and means for reversing ,the phase of the distortion components in said amplified signal. l

43. In an' electrical signaling system, an amplifier, an input circuit and an output circuit therefor, an incoming line connected tosaid input circuit, an o'utgoing line connected to said output circuit, a second amplifier of smaller capacity than said rst amplifier, means for coupling said second amplifierto said output circuit, means for coupling said second amplifier to said incoming line, and means for coupling the output circuit of said first amplifier4 to the input 'circuit of saldi second amplifier for impressing on said second amplifier distortion currents produced in said,

rst amplifier, the signal currents being neutralized in the input circuit' of said second ampliner. 44. A wave translating system comprising a main amplifying device producing wanted and unwanted waves, an 'auxiliary amplifying device for amplifying said unwanted waves, means for connecting the output of said main amplifying 65 fying device to the input of said `auxiliary am-y plifying device, and meansl'comprlsingaconnection from the output of saidauxiliary amplifying device to said main amplifying device for causing said unwanted waves,- amplified by said auxiliary amplifying device 'to be transmitted from 

